Modern buildings generally have large areas of glass and a wide range of internal temperature requirements, with both internally- and externally-generated heat loads. This diversity necessitates zone temperature control and high levels of air purity in order to ensure adequate comfort levels even with high occupation densities of people and equipment. Internally generated heat loads contribute to a large extent to the total cooling load or the total heating load. The main internal heat sources being electrical and electronic equipment and high illumination densities.
Localised climate control becomes necessary in large open-plan areas where individual workstations or equipment positions may require different temperatures. It is becoming more and more common to find people and equipment in the same office, requiring variation in thermal provision both in terms of Watts per square meter and seasonal changes. High-technology areas, such as computer rooms and control rooms, normally require air conditioning even during the winter since the heat produced by the equipment normally exceeds natural heat loss. There is therefore the need for a heating and air conditioning system which can effectively control conditions in the building and which has the flexibility to adapt to the range of needs over the various areas and in different seasons. Independent systems are normally used for the climate control of different areas, excluding the possibility of synergy and of intelligent control. There may be simultaneous demand for heating and cooling, each managed independently with significant energy wastage.
Furthermore, modern buildings have to be designed so as to enable a high flexibility of space configuration and occupation. It follows that space configuration and occupation can change many times over the life of a building and it is therefore important to ensure that air-condition systems can be easily adapted to such changes.